DIELECTRIC MATERIALS OF THE Bi3SbO7 TYPE

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DIELECTRIC MATERIALS OF THE Bi3SbO7 TYPE

M. Manier, J. Mercurio, D. Mercurio, B. Frit

To cite this version:

M. Manier, J. Mercurio, D. Mercurio, B. Frit. DIELECTRIC MATERIALS OF THE Bi3SbO7 TYPE.

Journal de Physique Colloques, 1986, 47 (C1), pp.C1-907-C1-911. �10.1051/jphyscol:19861140�. �jpa-

00225539�

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JOURNAL DE PHYSIQUE

Colloque Cl, supplément au n°2, Tome 47, février 1986 page cl-907

DIELECTRIC MATERIALS OF THE Bi

3

SbO

?

TYPE

M. MANIER, J . P . MERCURIO, D. MERCURIO a n d B . FRIT

Laboratoire de Chimie Minérale Structurale, L.R. C.N.R.S. 320, U.E.R. des Sciences, 123, Avenue Rlbert Thomas, F-87060 Limoges Cedex, France

Résumé - Un oxyde mixte de bismuth e t d'antimoine Bi3Sb07 a été i s o l é au sein du système Bi2°3

-

Sb205. L'étude par d i f f r a c t i o n X e t analyse thermique d i f f é r e n t i e l l e a montré que ce composé présente une t r a n s f o r m a t i o n polymor- phique vers 1050°C. Les deux v a r i é t é s ont une s t r u c t u r e c r i s t a l l i n e dérivée de l a f l u o r i n e e t v o i s i n e de c e l l e de Ln3Sb07- Leurs s t a b i l i t é s r e l a t i v e s ont été étudiées pour des s o l u t i o n s s o l i d e s Bi3-xLn

x

Sb07 avec Ln = La, Nd e t Gd. Les c a r a c t é r i s t i q u e s d i é l e c t r i q u e s mesurées à basse fréquence e t dans l e domaine hyperfréquence montrent que Bi3Sb07 p o u r r a i t s e r v i r de composé de base pour l a r é a l i s a t i o n de nouveaux résonateurs d i é l e c t r i q u e s microondes.

Abstract - A bismuth antimony oxide Bi3Sb07 has been i s o l a t e d in the Bi203- Sb205 system. DTA and X-ray diffraction a n a l y s i s have shown t h a t t h i s com- pound undergoes a polymorphic transformation a t about 1050°C. Both v a r i e t i e s have a f l u o r i t e r e l a t e d s t r u c t u r e close to the Lri3Sb07 one. The r e l a t i v e s t a - b i l i t y of the two polymorphs has been studied for the Bi3-xLnxSb07 s o l i d s o - l u t i o n s where Ln = La, Nd and Gd. Low and hyperfrequency measurements of the d i e l e c t r i c constant, temperature coefficient and d i e l e c t r i c losses have been performed on s i n t e r e d ceramics between room temperature and 100°C. The r e - sults'show t h a t Bi3Sb07 should be a basic compound for the elaboration of new microwave d i e l e c t r i c r e s o n a t o r s .

INTRODUCTION

The constant development of microwave i n t e g r a t e d c i r c u i t s makes necessary the elabo- ration of systems which can be used in the m i l l i m e t r i c or centimetric frequency range. Among these devices, d i e l e c t r i c resonators are more and more successfull due to t h e i r r e l a t i v e small dimensions and t h e i r a b i l i t y to be used both in passive and a c t i v e systems. As an example, a t 4 GHz a cylindrical m e t a l l i c cavity must be 90 mm in diameter and 43 mm in height whereas the dimensions of a d i e l e c t r i c resonator with e

r

= 38 used at the same frequency would be 12,5 mm in diameter and 6,25 mm in height only.

However the elaboration of d i e l e c t r i c resonators needs materials with a good tempera- t u r e s t a b i l i t y of the resonant frequency (in the ppm/°C range) and low d i e l e c t r i c losses ( 10-4) at high frequency. The number of presently available materials i s q u i t e small, e . g . Ba2Tig020, (Zr,Sn)Ti04, BaMgl/3Ta2/303, BaZrl/3Ta2/303, BaO-PbO- Nd205-Ti02 / l , 2 , 3 , 4 , 5 , 6 , 7 / .

Investigations in the Bi203-Sb205 system led us t o i s o l a t e a new bismuth antimony oxide with Bi3Sb07 formula ^ . P r e l i m i n a r y experiments have shown t h a t the d i e l e c - t r i c c h a r a c t e r i s t i c s of t h i s compound should correspond to the above mentioned c r i - t e r i a for d i e l e c t r i c resonators. Moreover i t seemed of i n t e r e s t to i n v e s t i g a t e some derivated compounds in order to modulate both d i e l e c t r i c constants and temperature c o e f f i c i e n t s .

Bi3Sb07 melts congruently a t a temperature close to 1120°C. I t undergoes a r e v e r s i b l e

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19861140

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JOURNAL DE PHYSIQUE

polymorphic transformation a 2 6 a t about 1050-1060°C. Nevertheless t h e high tempera- t u r e 6 phase can be s t a b i l i z e d i n t h e metastable s t a t e by quenchinn. X-ray p a t t e r n s of t h e two v a r i e t i e s , as do t h e orthorhombic LngSb07 ones, show s t r o n g l i n e s charac- t e r i s t i c o f a d i s t o r t e d f l u o r i t e - l i k e s u b l a t t i c e o f &-Biz03 type /TAIRI, A . , CHAMPAR- NAUD-MESJARD, J.C., MERCURIO, 0. and FRIT, B . , t o be published/. For t h e two poly- morphs, lanthanide s u b s t i t u t i o n f o r bismuth i s p o s s i b l e b u t i n both cases r a t h e r low ( 0

<

x 6 0.05 f o r Big-xLaxSbO7, 0

<

x a 0.10 f o r Bi3-xLnxSb07 w i t h Ln

=

Nd, Sm, Gd, Eu) . DTA experiments (500°C/h) showed t h a t t h e t r a n s i t i o n temperature s l i ~ h t l y de- creases (max : 30°C) when the s u b s t i t u t i o n c o n t e n t s i n c r e a s e s b u t does not depend on t h e n a t u r e o f t h e s u b s t i t u t e d l a n t h a n i d e .

DIELECTRIC PROPERTIES

-

D i e l e c t r i c p r o p e r t i e s o f t h e synthezised compounds were measured both a t low f r e - quency and i n t h e hyperfrequency range between room temperature and 100°C.

Weighed q u a n t i t i e s of reagent grade BizO3, SbZO3 and r a r e - e a r t h oxides were mixed and ground i n an agate mortar and c a l c i n e d f o r 48 hours a t 600°C. A f t e r grinding t h e reacted mixtures were heated again f o r 20 hours a t 850°C.

The weighed oxides were dissolved i n HC1 6 M and t h e mixed o x a l a t e s were coprecipi- t a t e by adding an excess o f an aqueous s o l u t i o n o f o x a l i c a c i d a t pH 10. A f t e r washing with d i s t i l l e d w a t e r and drying f o r several hours a t llO°C, t h e c o p r e c i p i t a - ted powders were calcined a t 500-700°C f o r 3 hours and then heated f o r 15 hours a t 800 -900" C .

Fig. 1. Scanning e l e c t r o n micrographs of polished ( l e f t ) and chemical l y etched ( r i g h t )

ceramics obtained by s o l i d s t a t e reaction ( a ) and from c o p r e c i p i t a t e d powders ( b ) .

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I t must be noticed t h a t o b t a i n i n g e i t h e r t h e

a

o r t h e B polymorph s t r o n g l y depends on t h e experimental conditions

:

t h e

a

polymorph was obtained pure

- f o r temperatures lower than about 950°C by s o l i d s t a t e r e a c t i o n s

- f o r temperatures lower t h e i r 870°C only by t h e wet method.

The l a r g e d i f f e r e n c e s between t h e phase transformation temperatures given by DTA and t h e temperatures used i n t h e thermal t r e a t m e n t s a r e obviously k i n e t i c i n c h a r a c t e r . Ceramic samples f o r die1 e c t r i c measurements were prepared by n a t u r a l s i n t e r i n g . Af- t e r grinding, t h e powders were uniaxialy cold-pressed a t 2 kbar i n a s t e e l d i e . The as-obtained d i s k s o r c y l i n d e r s were then s i n t e r e d i n a i r f o r 20 hours a t 900-970°C.

Typical dimensions o f t h e s i n t e r e d bodies were 8-10 mm i n diameter, 1 and 8 mm t h i c k f o r low and hyperfrequency c h a r a c t e r i z a t i o n r e s p e c t i v e l y . The apparent d e n s i t i e s c a l c u l a t e d from dimension measurements o r by t h e h y d r o s t a t i c method a r e i n t h e range 90-96 % o f t h e o r e t i c a l d e n s i t i e s and depend only s l i g h t l y on t h e composition.

Scanning e l e c t r o n microscopy observations of polished and etched B i 3Sb07 samples a r e given i n f i g u r e 1. All the samples present holes on t h e i r s u r f a c e s , t h e o r i g i n of which is c e r t a i n l y r e l a t e d t o some Biz03 o r Sb205 l o s s although no s i g n i f i c a n t weight l o s s was observed a f t e r s i n t e r i n g . Hicrographs of chemically etched ceramics show t h a t f o r samples obtained by s o l i d s t a t e r e a c t i o n t h e g r a i n s a r e well c r i s t a l - l i z e d and separated ; those obtained from c o p r e c i p i t a t e d powders show l e s s e r grain growth i n r e l a t i o n with a lower p o r o s i t y .

2. D i e l e c t r i c measurements

In t h e low frequency range, d i e l e c t r i c constants

cr and

d i e l e c t r i c l o s s e s t g

6

were measured between room temperature and 100°C with a B 905 Wayne Kerr RLC automatic bridge a t 103 and 104 Hz. A f t e r being e l e c t r o d e d with a low temperature s i l v e r p a s t e coating, t h e samples were heated up t o llO°C o v e r n i g h t .

Table I . Low frequency (10 kHz) c h a r a c t e r i s t i c s o f Bi3Sb07 and Bij-xLnxSb07

ceramics. (CO and VS r e f e r t o t h e coprecipi tation and t h e solid s t a t e methods r e s p e c t i v e l y ) .

--

Table I gives t h e d i e l e c t r i c c h a r a c t e r i s t i c s a t 10 kHz obtained f o r several BijSbO7 samples a s we1 1 as f o r some s e l e c t e d r a r e - e a r t h s u b s t i t u t e d s o l i d s o l u t i o n s . The ce- ramics always correspond t o t h e low-temperature Bi3Sb07 polymorph.

Compound

B i 3Sb07

Bi2.95La0.05Sb07 B i 2.95La0.05Sb07 Bi2.95Ndo.05Sb07 Bi2.95Nd0.05Sb07 Bi2.90Nd0. 10Sb07 Bi2.95Gd0.05Sb07 Bi2.90Gd0. 10Sb07

All t h e samples have d i e l e c t r i c constants l y i n g i n t h e range 28-38 and d i e l e c t r i c l o s s e s between 20 and 40.10-4. Temperature c o e f f i c i e n t s of capacitance, c a l c u l a t e d between room temperature and 100°C a r e a l l p o s i t i v e and show q u i t e a l a r g e disper-

Sample

CO 5 CO 6 VS13 VS 15 VS 11 CO 2 CO 3 CO 5 CO 1 CO 5

Relative d e n s i t y

% (k0.1) 93.7 94.0 94.8 91.1 87.4 92.3 87.0 89.3 92.5 91.3

D i e l e c t r i c constant

E r

(f0.1) 30.0 36.6 36.3 27.7 30.9 35.0 30.5 31.2 31.1 34.6

D i e l e c t r i c l o s s 104tg6 ( + I )

25 20 14 20 20 35 30 40 20 20

Temperature coef.

o f capacitance r c (ppm/OC)

110 106 5 8 9 1 105

9 2

160

180

105

300

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JOURNAL DE PHYSIQUE

s i o n which seems t o be r e l a t e d as f o r t h e d i e l e c t r i c c o n s t a n t s t o t h e p o r o s i t y o f t h e samples.

D i e l e c t r i c c h a r a c t e r i s t i c s a t microwave frequency were measured by t h e d i e l e c t r i c r e s o n a t o r method. D i e l e c t r i c c o n s t a n t s were c a l c u l a t e d f r o m t h e r e s o n a n t frequency o f t h e TEols r e s o n a n t mode and t h e d i e l e c t r i c l o s s e s were d e r i v a t e d f r o m t h e r e s o - n a n t c u r v e /9/. Table I 1 g i v e s t h e microwave c h a r a c t e r i s t i c s o f some Bi3Sb07 ceramic r e s o n a t o r s .

Table 11. Microwave c h a r a c t e r i s t i c s o f some BigSbO7 ceramics (CO and VS r e f e r t o t h e c o p r e c i p i t a t i o n and t h e s o l i d s t a t e methods r e s p e c t i v e l y ) .

Bi3Sb07

CO 6

A t about 6.6 GHz t h e d i e l e c t r i c constants a r e c l o s e t o 40 ( t h e a b s o l u t e values o f

^E

a t microwave frequency cannot be compared t o t h o s e o b t a i n e d a t low frequency) and t h e d i e l e c t r i c l o s s e s i n t h e range 5.10-4 - 7.10-4. The temperature c o e f f i c i e n t s o f t h e r e s o n a n t frequency

~f

strong1 y depend on t h e ceramic e l a b o r a t i o n . Nevertheless these r e s u l t s f i t q u i t e w e l l t h e r e l a t i o n between ~ f ,

^{T C}

and

^T,

( r e s p e c t i v e l y tem- p e r a t u r e c o e f f i c i e n t s o f c a p a c i t a n c e and d i e l e c t r i c c o n s t a n t ) and t h e l i n e a r t h e r a l expansion c o e f f i c i e n t a

^{( 1}

10 - 20 ppm/OC)

VS 11

T

+ 2 ~ ~ + 2 a = O and r C = r

+ a

CONCLUSIONS

r e s o n a n t frequency

20" C 6876 MHz

30" C

Ceramics w i t h d i e l e c t r i c constants l y i n q i n t h e range 28-40 and w i t h l o w l o s s e s a t microwave f r e q u e n c i e s , were o b t a i n e d by s i n t e r i n q B i ~ S b 0 7 powders a t temperature below 1000°C. Rare-earth s u b s t i t u t i o n s f o r bismuth do n o t s t r o n g l y a f f e c t t h e d i e - l e c t r i c c h a r a c t e r i s t i c s .

6645.7 MHz 35" C

Experiments i n o r d e r t o improve t h e microwave p r o p e r t i e s ( h o t - p r e s s i n g , use o f some a d d i t i v e s w i t h s u i t a b l e c h a r a c t e r i s t i c s ) a r e now i n progress.

Temperature c o e f f i c i e n t o f resonant frequency

T~

(ppm/OC)

-69.2

Acknowledgements :

-31.3

The a u t h o r s thank J.C. Mage and J.P. Ganne (LCR Thomson CSF, Orsay, France) f o r m i - crowave measurements.

Die1 e c t r i c con;tant

r

40.1 D i e l e c t r i c l o s s t g

6

( + 2 . 1 0 - ~ )

7. 42.1 7 . 1 0 - ~

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REFERENCES

/1/ Plourde, J.K., Linn. D.F., O'Bryan, J r . H.M. and Thomson, Jr., J.T., J. Amer.

Ceram. Soc. 58 r9-10 (1975) 418.

754. 4

/2/ P1ourdeTJ.X. an Chung-Li Ren, IEEE Trans. Microware Theory Tech. 9 (1981) /3/ Mage, J.C., Rev. Tech. Thomson-CSF, 14

L 624.

/4/ Nomura, S., Toyama, K. and Kaneta, K K 21 [1q - (1982)

- - - .